Radiation therapy involves delivering tumoricidal doses of radiation to localized regions of the body. Stereotactic radiation therapy, also called radiosurgery, may be used to treat tumors in the brain, breast, head, neck, lung, liver, pancreas, spine, and prostate. Various tumor localization techniques may be used to precisely determine the location of tumor(s) to help ensure that a high dose of radiation is delivered to the tumor(s), while sparing healthy, non-cancerous tissue. For example, on-board imaging technologies such as single and stereoscopic x-ray imaging, kilovoltage and megavoltage CT imaging, implantable fiducial markers and transponders, ultrasound imaging. MRI, and others may help to improve the efficacy of radiation therapy by gathering tumor location information such that a radiation beam may be specifically targeted at the tumor region. Various radiation beam-shaping techniques may also be used to help direct radiation precisely at the tumor(s) to be treated, while reducing the radiation exposure to surrounding tissue.